Synthesis of 2-Alkoxy(aroxy)-3-substituted Quinolines by DABCO-Promoted Cyclization of o-Alkynylaryl Isocyanides

Stereoselective protecting-group-free synthesis of alkyl glycosides using dibenzyloxy triazine type glycosyl donors

Chemical O-glycosylation is a key step for the synthesis of sugar-containing molecules such as glycolipids. However, traditional carbohydrate chemistry is characterized by extensive use of protective groups, resulting in laborious manipulations and poor atom economy. Here, we present a protecting-group-free glycosylation strategy employing dibenzyloxy-1,3,5-triazin-2-yl glycosides (DBT-glycosides) as glycosyl donors. The DBT-glycosyl donors could be prepared directly through an alkaline nucleophilic substitution from unprotected sugars in aqueous media. The O-glycosylation of alcohols by using DBT-glycosyl donors has been carried out under mild hydrogenolytic conditions, affording the corresponding alkyl glycosides stereo-selectively in good yields.

Base-catalyzed diastereodivergent thia-Michael addition to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones

Base-catalyzed diastereodivergent thia-Michael addition of thiols to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones is reported. By tuning the base-catalyst (i-Pr2NEt, DABCO, or P2-t-Bu), a range of chiral thia-Michael adducts was synthesized in good yields with high diastereoselectivities. A plausible mechanism was proposed on the basis of the experimental results. This work is complementary to the existing methods offering advantages, e.g., switchable diastereoselectivity using a readily synthesized chiral starting material, a cheap and readily available base catalyst, and a simple and practical operation, enabling synthetic application in organic synthesis.

Bicyclic Amidine-Triggered Cyclization of o-Alkynylisocyanobenzenes: Synthesis of Lactam-Derived Quinolines

Efficient access to the synthesis of lactam-derived quinoline through a bicyclic amidine-triggered cyclization reaction from readily prepared o-alkynylisocyanobenzenes has been developed. The reaction was initiated by nucleophilic attack of the bicyclic amidines to o-alkynylisocyanobenzenes, subsequently with intramolecular cyclization to produce a DBU-quinoline-based amidinium salt, followed by hydrolysis to afford the lactam-derived quinoline in moderate to good yields.

Copper-Catalyzed Cyclization of 2-Alkynylanilines to Give 2-Haloalkoxy-3-alkyl(aryl)quinolines

Herein we describe a method to produce 2-haloalkoxy-3-substituted quinolines via the cyclization of 2-alkynylanilines with TMSCF₃ and THF. This synthetic method uses inexpensive and easy-to-handle TMSCF₃ and employs a commercially available CuI catalyst to transform a broad range of 2-alkynylanilines into versatile 2-difluoromethoxy-3-substituted quinolines and 2-iodoalkoxy-3-substituted quinolines with excellent chemoselectivity.

An expedient route to tricyanovinylindoles and indolylmaleimides from o-alkynylanilines utilising DMSO as a one-carbon synthon

A Pd(ii)/Cu(ii) catalysed domino synthesis of tricyanovinylindoles has been achieved using DMSO as a one-carbon synthon. The reaction proceeds via the construction of 2-aryl-3-formyl indole followed by sequential addition of malononitrile and a CN resulting in two C-C, one C[double bond, length as m-dash]C and one C-N bonds in the final product. Furthermore, post-synthetic modification results in the unprecedented formation of 4-cyano-3-indolylmaleimides. Photophysical studies of selected compounds show emission in the visible range.

Organocatalyzed Synthesis of Functionalized Quinolines

As one of the most widely investigated compound skeleton, quinolines possess important medicinal and biological activities. As such, a great number of literatures, including reviews, have reported various methodologies to construct quinolines. Recently, organocatalyzed reactions have attracted the attention of organic chemists due to its being "green" because the reactions avoid the use of toxic metals. In this review, various distinctive contributions are surveyed with specific emphasis on organocatalyzed reactions for quinoline core constructions.

Synthesis of 3-substituted quinolin-2(1H)-ones via the cyclization of o-alkynylisocyanobenzenes

A facile synthesis of various functionalized 3-substituted quinolin-2(1H)-ones through Ag(i) nitrate-catalyzed cyclization of o-alkynylisocyanobenzenes is described. The reaction allows rapid and convenient access to 3-substituted quinolin-2(1H)-one scaffolds in moderate to good yields.

Expedient approach to synthesis of 4-hydroxy-2-(trifluoromethyl) quinolines through an intramolecular cyclization of ethyl 2-cyano-4,4,4-trifluoro-3 (arylamino)but-2-enoate derivatives

Ethyl 2-cyano-4,4,4-trifluoro-3-(phenylamino)but-2-enoates have been synthesized by reaction of ethyl 2-cyanoacetate with trifluoroacetimidoyl chloride derivatives using sodium hydride in acetonitrile by conventional and microwave irradiation methods. Then, intramolecular cyclization of these products in nitrobenzene under reflux conditions afforded a new series of substituted (trifluoromethyl)quinoline-3-carbonitrile derivatives in quantitative yields.

To each his own: isonitriles for all flavors. Functionalized isocyanides as valuable tools in organic synthesis

The term functionalized isocyanides refers to all those isocyanides in which a neighbouring functional group can finely tune the reactivity of the isocyano group or can be exploited in post-functionalization processes. In this manuscript, we have reviewed all the isocyanides in which the pendant functional group causes either deviation from or reinforces the normal reactivity of the isocyano group and categorized them to highlight their common features and differences. An analysis of their synthetic potential and the possible unexplored directions for future research studies is also addressed.

Sulfinates and thiocyanates triggered 6-endocyclization ofo-alkynylisocyanobenzenes

An efficient synthesis of 2-sulfonyl- and 2-thiocyanato-3-substituted quinolines through sequential nucleophilic addition/cyclization ofo-alkynylisocyanobenzenes is described.

Base-Promoted Synthesis of Quinoline-4(1H)-thiones from o-Alkynylanilines and Aroyl Isothiocyanates

A base-promoted synthesis of quinoline-4(1H)-thiones has been accomplished from the in situ generated o-alkynylthiourea, obtained by reacting o-alkynylanilines with aroyl/acyl isothiocyanates. A 6-exo-dig S-cyclization of the in situ generated thiourea is followed by a rearrangement to give quinoline-4(1H)-thiones.

Organocatalytic activation of isocyanides: N-heterocyclic carbene-catalyzed enaminone synthesis from ketones

The first example of the use of an N-heterocyclic carbene (NHC) as an organocatalyst for the activation of isocyanides was demonstrated. On the basis of previous reports on the interaction between NHCs and isocyanides, we developed a catalytic cycle involving transient imidoyl intermediate. The reaction of ketones with isocyanides produced the corresponding enaminones with high efficiency. Control experiments suggested a novel role for the carbene in the activation of isocyanides, and a proton transfer process was found to be crucial for the generation of two activated species in the catalytic cycle. Various enaminones, some of which are not easily accessible by other methods, were synthesized in excellent yields. This study clearly demonstrates the potential of the nucleophilic activation of isocyanides in the expansion of their reactivity scope.

DABCO-catalyzed consecutive one pot four-component protocol for the synthesis of a novel class of (Z)-5-(3-hydroxy-2-oxoindolin-3-yl)-2-iminothiazolidin-4-ones

A DABCO catalyzed, novel and efficient one-pot, four component protocol has been developed for the synthesis of (Z)-5-(3-hydroxy-2-oxoindolin-3-yl)-2-iminothiazolidin-4-one scaffolds under metal-free conditions.

A transition-metal-free synthesis of arylcarboxyamides from aryl diazonium salts and isocyanides

A transition-metal-free carboxyamidation process, using aryl diazonium tetrafluoroborates and isocyanides under mild conditions, has been developed. This novel conversion was initiated by a base and solvent induced aryl radical, followed by radical addition to isocyanide and single electron transfer (SET) oxidation, affording the corresponding arylcarboxyamide upon hydration of the nitrilium intermediate.

Quinoline: A versatile heterocyclic

Quinoline or 1-aza-naphthalene is a weak tertiary base. Quinoline ring has been found to possess antimalarial, anti-bacterial, antifungal, anthelmintic, cardiotonic, anticonvulsant, anti-inflammatory, and analgesic activity. Quinoline not only has a wide range of biological and pharmacological activities but there are several established protocols for the synthesis of this ring. The article aims at highlighting these very diversities of the ring.